1. Princeton Plasma Physics Laboratory 1 , Princeton, New Jersey 08543, USA
2. Laboratory for Laser Energetics, University of Rochester 2 , Rochester, New York 14623, USA
3. General Atomics 3 , P.O. Box 85608, San Diego, California 92186-5608, USA
4. Department of Applied Physics and Applied Mathematics, Columbia University 4 , New York, New York 10027, USA